The impact of OAE 1a on marine biota deciphered by size variations of coccoliths |
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| Institution: | 1. Institut für Geologie, Leibniz Universität Hannover, Callinstraβe 30, 30167 Hannover, Germany;2. Institut de Physique du Globe de Strasbourg, EOST, Université de Strasbourg, 1 rue Blessig, 67084 Strasbourg Cedex, France;3. Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, Universitätstrasse 150, 44801 Bochum, Germany;4. Department of Environment, Earth and Ecosystems, The Open University, Milton Keynes MK7 6AA, United Kingdom;5. Institut für Erd- und Umweltwissenschaften, Universität Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam-Golm, Germany;6. Institut de Géologie et Paléontologie, Université de Lausanne, Géopolis, 1015 Lausanne, Switzerland;1. Institute for Geology, Mineralogy and Geophysics, Ruhr-Universität Bochum, Universitätsstr. 150, 44801 Bochum, Germany;2. University of Milano, via Mangiagalli 34, 20133 Milano, Italy |
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| Abstract: | The early Aptian Oceanic Anoxic Event 1a (OAE 1a; ～120 Ma) was caused by a global perturbation of the Early Cretaceous climate. It supposedly affected the composition of the marine biosphere, including the primary producers. This study aims at using the size evolution of three species of coccolithophores (Biscutum constans, Zeugrhabdotus erectus and Watznaueria barnesiae) for better understanding the impact of the OAE 1a on primary producers. A total of 30 samples derived from three sites, which cover the upper Barremian–lower Aptian interval, have been analyzed from the North Sea and the Lower Saxony Basin. The sections expose near-shore and shallow marine sediments.The measured data of B. constans and Z. erectus are characterized by a size decrease synchronous to the negative carbon isotope excursion. This size reduction marks the early phase of the OAE 1a, more precisely the carbon isotope segment C3. Coccolith sizes recover to pre-OAE 1a values in the aftermath of this brief interval. The short termed size reduction is seen as a reaction of specific nannofossil taxa to an increase in humidity during the early phase of OAE 1a. Due to high weathering rates and a substantial run-off, the amount of detrital material transported into the marine system increased significantly. Consequently light availability diminished in the surface waters, causing habitat changes for the photoautotrophic primary producers. Light-sensitive species like B. constans and Z. erectus adjusted by forming smaller skeletons, thereby reducing their size. This strategy allowed for dwelling in shallower water depth and thus compensated for the decrease in sun light. The sizes of W. barnesiae in contrast remain stable throughout the entire OAE 1a interval. W. barnesiae was not affected by these environmental shifts and is thus interpreted as being robust with respect to changes of the sun light. |
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| Keywords: | Calcareous nannofossils Oceanic Anoxic Event 1a (OAE 1a) Biometry Barremian Aptian |
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